D'addario's XL strings have been my no.1 choice for National steel bodied resonator guitar. These flat strings give the guitar a very unique, deep and mellow sound, and a very smooth feel -- interesting for both fingerstyle and noiseless slide playing. It might not be for everybody, and after a while I've found myself using the EJ22 set more regularly instead of this one, but still I find this flat set very usable for certain kind of resonating approach. The quality is very fine.